Switch reduction in a cordless power tool

ABSTRACT

A battery pack may include at least one battery cell, a discharge switch coupled to the at least one battery cell, and monitoring and control circuitry responsive to a position of a trigger of an associated cordless power tool to provide a control signal to the discharge switch. The discharge switch may be responsive to the control signal to control a discharge current provided to a load of the cordless power tool. The load may be a motor driving an element of the cordless power tool.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/568,038, filed May 4, 2004, the teachings of which are incorporated herein by reference.

FIELD

The present disclosure relates to cordless power tools and, more particularly, to reduction of switches in a cordless power tool.

BACKGROUND

A wide variety of cordless power tools are available that may be utilized in different applications such as construction applications, fire and rescue applications, etc. Some examples of cordless power tools include, but are not limited to, cordless drills, cordless circular saws, cordless reciprocating saws, cordless sanders, cordless screwdrivers, and flashlights. Cordless power tools may utilize a rechargeable battery pack for providing power to operate the tool. The rechargeable battery pack may be readily removed from the cordless power tool and coupled to an external battery charger for charging purposes.

The battery pack may include one or more battery cells. The battery pack may also include monitoring circuitry to monitor parameters such as cell voltage levels, discharge current, and charging current. The battery pack may also include switches such as a discharge switch which may be opened in response to the monitoring circuitry detecting some overload condition. Another control switch may be utilized in the cordless power tool to control a level of discharge current supplied to a load of the cordless power tool. For example, the control switch may be a speed control switch to control the speed of an element of the cordless power tool. This switch may be a relatively expensive switch requiring overload protection. Accordingly, there is a need in the art to eliminate the speed control switch yet still provide similar functionality.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a battery pack. The battery pack may include at least one battery cell, a discharge switch coupled to the at least one battery cell, and monitoring and control circuitry responsive to a position of a trigger of an associated cordless power tool to provide a control signal to the discharge switch, the discharge switch responsive to the control signal to control a discharge current provided to a load of the cordless power tool.

According to another aspect of the invention, there is provided a cordless power tool. The cordless power tool may include a load, a trigger, and a battery pack. The battery pack may include at least one battery cell to provide power to the load. The battery pack may further include a discharge switch coupled to the at least one battery cell, and monitoring and control circuitry responsive to a position of the trigger to provide a control signal to the discharge switch. The discharge switch may be responsive to the control signal to control a discharge current provided to the load.

According to yet another aspect of the invention there is provided a method. The method may include monitoring a position of a trigger of a cordless power tool, and controlling a state of a discharge switch of a battery pack in response to the position of the trigger to control a discharge current provided to a load of the cordless power tool.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the claimed subject matter will become apparent as the following Detailed Description proceeds, and upon reference to the Drawings, where like numerals depict like parts, and in which:

FIG. 1 is a perspective view of a cordless power tool;

FIG. 2 is a diagram of a power supply system of the cordless power tool of FIG. 1;

FIG. 3 is a diagram consistent with FIG. 2 where the load is a motor driving an element of the cordless power tool;

FIG. 4 is another diagram a power supply system for the cordless power tool of FIG. 1;

FIG. 5 is a diagram of an embodiment of the monitoring and control circuitry; and

FIG. 6 is a flow chart of operations consistent with an embodiment.

Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the claimed subject matter be viewed broadly.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of a cordless power tool 100. The cordless power tool 100 is illustrated as a cordless drill and may be described as such in relation to embodiments herein. However, the cordless power tool 100 may be any type of cordless power tool including, but not limited to, a cordless circular saw, a cordless reciprocating saw, a cordless sander, a cordless screwdriver, and a flashlight. The cordless power tool may include a rechargeable battery pack 102 for providing power to operate the tool 100. The rechargeable battery pack 102 may be readily removed from the cordless power tool 100 and coupled to an external battery charger for charging purposes. The cordless power tool 100 may also include a trigger 104. For the drill, a user may depress and release the trigger 104 to control the speed of the chuck 142. For other tools such as a flashlight, a user may position a trigger to control a level of illumination from the flashlight.

FIG. 2 is a diagram of a power supply system 200 of the cordless power tool of FIG. 1. The power supply system 200 may include the battery pack 102, a load 240, the trigger 104, and tool identification (ID) circuitry 230. As used in any embodiment herein, “circuitry” may comprise, for example, singly or in any combination, hardwired circuitry, programmable circuitry, state machine circuitry, and/or firmware that stores instructions executed by programmable circuitry.

The battery pack 102 may include one or more battery cells 203 to provide power for the system 200. The battery cells 103 may be lithium ion cells in one embodiment. The battery pack 102 may provide power to the load 240 via the discharge switch 209. In one embodiment, the discharge switch may be a field effect transistor (FET). The battery pack 102 may also include monitoring and control circuitry 208. The monitoring and control circuitry 208 may measure one or more of battery pack current, temperature, and cell voltage levels for each battery cell.

The monitoring and control circuitry 208 may compare measured values to associated threshold levels and identify an overload condition if one of the measured quantities is greater than or equal to the associated threshold level. For example, an overload condition may be a discharge current greater than or equal to a threshold representative of a maximum discharge current. In another example, an overload condition may be a charging current level to the battery cells 203 greater than or equal to a threshold representative of a maximum charging current. In yet another example, an overload condition may be a voltage level of a battery cell greater than or equal to a voltage threshold. In yet another embodiment, an overload condition may be a temperature of a component greater than or equal to a temperature threshold. Upon detection of an overload condition, the monitoring and control circuitry 208 may provide an output control signal to protect components of the power supply system 200. The output control signal may be provided to one or more switches within the battery pack 102 or may be provided as a control input to other circuitry located outside the battery pack 102 via path 127. In one embodiment, the output control signal may be provided to the discharge switch 209 to open the switch 209 where the overload condition is a discharge current from the battery cells 203 greater than or equal to a maximum discharge current threshold.

The monitoring and control circuitry 208 may also be responsive to the position of the trigger 104 to provide a control signal to the discharge switch 209. The control signal may be a pulse width modulated (PWM) signal 218 in one embodiment and the discharge switch 209 may be responsive to the duty cycle of the PWM signal 218 to control the discharge current. The PWM signal 218 may operate at a fixed frequency, e.g., such as 5 to 10 kilohertz (KHz). As the duty cycle of the PWM signal is increased, the ON time of the discharge switch 209 may be increased and hence the level of discharge current provided to the load 240 may be increased. Similarly, as the duty cycle of the PWM signal is decreased, the ON time of the discharge switch may be decreased and hence the level of discharge current provided to the load 240 may be decreased.

The tool ID circuitry 230 may provide a tool identification signal to the monitoring and control circuitry 208. The tool identification signal may be representative of data particular to the cordless power tool such as a variety of power parameters of the particular cordless power tool. For example, the tool identification signal may specify a maximum discharge current of the particular cordless power tool. As another example, the tool identification signal may specify a thermal overload point of the cordless power tool. The tool ID circuitry 230 may include inexpensive passive components such as a paralleled resistor and capacitor in one embodiment or a simple fixed resistor in another embodiment. In addition, the tool ID circuitry 230 may provide a useful secondary indication that the battery pack 102 has been correctly plugged into the appropriate cordless power tool. In the absence of a proper tool identification signal, the battery pack 102 may deny discharge thereby improving system safety.

FIG. 3 is a diagram of a power supply system 300 consistent with the power supply system 200 of FIG. 2. Components of FIG. 3 similar to FIG. 2 are labeled as such and hence any repetitive description is omitted herein for clarity. The load 240 a in FIG. 3 may be a motor 340 configured to drive an element 142 through an associated gear train (not illustrated). As one example, the element 142 may be the chuck of the drill of FIG. 1 that holds a drill bit. Advantageously, a conventional speed control switch that may be located in the cordless power tool at the input side to the motor 340 has been eliminated. In its place, the discharge switch 209 may control a discharge current and hence a speed of the element 142 driven by the motor 340.

Speed select circuitry 316 may receive a signal from the trigger 104 representative of a position of the trigger 104 and hence a desired speed of the element 142 of the cordless power tool. The speed select circuitry 316 may then provide an input signal to the monitoring and control circuitry 208 of the battery pack 102 representative of the desired speed. The monitoring and control circuitry 208 may then provide a control signal to the discharge switch 209 to control the speed of the element 142 by controlling the discharge current provided to the motor 340.

In operation, a user of the cordless power tool may depress the trigger 104 a desired amount to control the speed of the element 142. In response to the position of the trigger 104, the speed select circuitry 316 may provide an input signal to the monitoring and control circuitry 208. The monitoring and control circuitry 208 may include a PWM generator that modifies the duty cycle of the PWM signal 218 in response to the input signal from the speed select circuitry 316. The PWM signal 218 may operate at a fixed frequency, e.g., such as 5 to 10 KHz. As the duty cycle of the PWM signal is increased, the ON time the discharge switch 209 may be increased and hence the speed of the element 142 of the cordless power tool is also increased. Similarly, as the duty cycle of the PWM signal is decreased, the ON time of the discharge switch 209 may be decreased and hence the speed of the element 142 of the power tool may be decreased. In one example, the duty cycle of the PWM signal may vary from about 10% (slow speed) to 75% (fast speed).

FIG. 4 is another diagram a power supply system for the cordless power tool of FIG. 1. The discharge switch 209 may be an FET Q1. The FET Q1 may be a metal oxide semiconductor field effect transistor (MOSFET) such as a p-channel MOSFET (PMOS) or n-channel MOSFET (NMOS). The battery pack 102 a may also include a plurality of battery cells 203-1, 203-2, 203-(n−1), and 203-n. The battery pack 102 a may supply power to a number of loads including a load 240 b illustrated as a motor winding. A diode 410 may be connected in parallel with the FET Q1 to permit charging current flow into the battery cells 203-1, 203-2, 203-(n−1), and 203-n and to prevent discharge current from the battery cells. The battery pack 102 a may include optional status indicators 406 to provide indication signals from the monitoring and control circuitry 208 of various detected conditions.

The speed select circuitry 316 a may include a variable resistor 454 in series with another resistor 452. The variable resistor 454 may be a potentiometer. A resistance value of the variable resistor 454 may be set in response to the position of the trigger 104. The resistance value of the variable resistor 454 may therefore be representative of a desired speed of the element 142 (see FIG. 3). The resistance value of the resistor 452 may be representative of a maximum discharge current rate. This speed select circuitry 316 a allows for inexpensive discharge limiting and/or variable power control for low cost cordless power tools such as flashlights. A third battery pack terminal 422 may be used by the monitoring and control circuitry 208 to receive information from the speed select circuitry 316 a on the desired speed. In turn, the monitoring and control circuitry 208 may provide a PWM signal 218 at a particular duty cycle to achieve the desired speed.

FIG. 5 is one embodiment 208 a of the monitoring and control circuitry 208. The monitoring and control circuitry 208 a may include a switch network 502, an analog to digital converter (ADC) 504, a processor 506, a driver 508, protection circuitry 524, and a PWM generator 510. The processor 506 may instruct the switch network 502 to select a particular battery cell 203-1, 203-2, 203-(n−1), or 203-n for monitoring. Individual analog cell voltage levels for each battery cell may then be sampled through the switch network 502. The sampled analog signals may then be converted into associated digital signals by the ADC 504 and provided to the processor 506. The processor 506 therefore receives digital signals from the ADC 504 representative of the voltage level of each battery cell 203-1, 203-2, 203-(n−1), and 203-n and may make comparisons to various voltage thresholds.

For example, during charging of the battery pack 102, the monitoring and control circuitry 208 a may monitor the cell voltage levels to determine if any of the cell voltage levels exceeds an over voltage threshold. If such a threshold is exceeded, the processor 506 may instruct some preventative action to be taken. In one instance, such preventative action may be to stop charging by providing a signal to the driver 508 to drive a particular switch open. In another example, during discharging of the battery pack 102, the monitoring and control circuitry 208 a may monitor the cell voltage levels to determine if any of the cell voltage levels is less than an under voltage threshold. If such an under voltage threshold level is reached, the processor 506 may instruct some preventative action to be taken. In one instance, such preventative action may be to stop discharging by providing a signal to the driver 508 to drive a particular switch open.

The processor 506 may also receive other signals from the protection circuitry 524. The protection circuitry 524 may generally monitor the current flowing into (charging mode) or out of (discharging mode) the battery pack 102 for various current overload conditions, e.g., over current or short circuit conditions, and alert the processor 506 of such conditions so that preventative action can be taken. For instance, a current sensing element such as sense resistor 404 (FIG. 4) may provide the protection circuitry 524 with a signal representative of the current level to or from the battery pack as that current level varies. The protection circuitry 524 may compare the current level to various thresholds and provide a signal to the processor notifying the processor of an over current condition or a short circuit condition so the processor 506 can take preventative action.

The PWM generator 510 may receive a signal from the speed select circuitry 316, 316 a and provide an output PWM signal to the discharge switch such as FET Q1 (see FIG. 4). The processor 506 may allow the PWM signal to control the state of the discharge switch until an overload condition occurs. When the overload condition occurs, e.g., excessive discharge current, the processor 506 may disable the PWM generator 510 and may instruct the driver 508 to open the discharge switch. As such, the monitoring and control circuitry 208 a can advantageously enable the PWM generator 510 to control the discharge switch 209 when appropriate and it can also disable the PWM generator 510 and open the discharge switch if an overload condition is detected.

FIG. 6 illustrates operations 600 according to an embodiment. Operation 602 may include monitoring a position of a trigger of a cordless power tool. Operation 604 may include controlling a state of a discharge switch of a battery pack in response to the position of the trigger to control a discharge current provided to a load of the cordless power tool.

Advantageously, elimination of a conventional speed control or load control switch provides cost savings and simplifies configuration complexity. Such speed or load control may be accomplished by a discharge switch in the battery pack. In addition, a cordless power tool may include tool ID circuitry. The tool ID circuitry may enable the battery pack to receive data about a particular tool that it may otherwise not be aware. Such data may include data of the maximum discharge current of the particular cordless power tool or a thermal overload point of the particular tool to name a couple. In addition, the tool ID circuitry could provide a useful secondary indication that the battery pack has been correctly plugged into the appropriate cordless power tool. In the absence of a proper tool identification signal, the battery pack could deny discharge thereby improving system safety

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described (or portions thereof, and it is recognized that various modifications are possible within the scope of the claims. Other modifications, variations, and alternatives are also possible. 

1. A battery pack comprising: at least one battery cell; a discharge switch coupled to said at least one battery cell; and monitoring and control circuitry responsive to a position of a trigger of an associated cordless power tool to provide a control signal to said discharge switch, said discharge switch responsive to said control signal to control a discharge current provided to a load of said cordless power tool.
 2. The battery pack of claim 1, wherein said load comprises a motor to drive an element of said cordless power tool, said motor receiving said discharge current controlled by said discharge switch, said discharge switch controlling a speed of said element driven by said motor by controlling said discharge current.
 3. The battery pack of claim 1, wherein said control signal comprises a pulse width modulated (PWM) signal and said discharge switch is responsive to a duty cycle of said PWM signal to control said discharge current.
 4. The battery pack of claim 1, wherein said monitoring and control circuitry monitors said discharge current and open said discharge switch if said discharge current is greater than or equal to a maximum discharge current threshold.
 5. The battery pack of claim 1, wherein said discharge switch comprises a field effect transistor (FET).
 6. A cordless power tool comprising: a load; a trigger; and a battery pack comprising at least one battery cell to provide power to said load, said battery pack further comprising a discharge switch coupled to said at least one battery cell, and monitoring and control circuitry responsive to a position of said trigger to provide a control signal to said discharge switch, said discharge switch responsive to said control signal to control a discharge current provided to said load.
 7. The cordless power tool of claim 6, wherein said load comprises a motor to drive an element of said cordless power tool, said motor receiving said discharge current controlled by said discharge switch of said battery pack, said discharge switch controlling a speed of said element driven by said motor by controlling said discharge current.
 8. The cordless power tool of claim 7, further comprising speed select circuitry responsive to said position of said trigger to provide an input signal to said monitoring and control circuitry of said battery pack.
 9. The cordless power tool of claim 8, wherein said speed select circuitry comprises a variable resistor in series with a resistor, wherein a resistance value of said variable resistor is set in response to said position of said trigger and is representative of a desired speed of said element, and wherein a resistance value of said resistor is representative of a maximum discharge current rate.
 10. The cordless power tool of claim 6, wherein said control signal comprises a pulse width modulated (PWM) signal and said discharge switch is responsive to a duty cycle of said PWM signal to control said discharge current.
 11. The cordless power tool of claim 6, wherein said monitoring and control circuitry monitors said discharge current and opens said discharge switch if said discharge current is greater than or equal to a maximum discharge current threshold.
 12. A method comprising: monitoring a position of a trigger of a cordless power tool; and controlling a state of a discharge switch of a battery pack in response to said position of said trigger to control a discharge current provided to a load of said cordless power tool.
 13. The method of claim 12, wherein said load comprises a motor to drive an element of said cordless power tool, said motor receiving said discharge current controlled by said discharge switch of said battery pack, said discharge switch controlling a speed of said element driven by said motor by controlling said discharge current.
 14. The method of claim 12, further comprising: monitoring said discharge current; and opening said discharge switch of said battery pack if said discharge current is greater than or equal to a maximum discharge current threshold.
 15. The method of claim 12, further comprising providing a tool identification signal to said battery pack once said battery pack is coupled to said cordless power tool, said tool identification signal representative of data particular to said cordless power tool.
 16. The method of claim of claim 15, wherein said data comprises a maximum discharge current of said cordless power tool.
 17. The method of claim of claim 15, wherein said data comprises a thermal overload point of said cordless power tool. 